They received commendations on the eve of the £2.6 million heist's 50th anniversary from chief constable Sara Thornton.

The robbery took place on August 8 1963, when a gang masterminded by Bruce Reynolds stopped the Glasgow-Euston overnight mail train as it passed through the Buckinghamshire countryside close to Cheddington.

Keith Milner, now 78, was the duty detective at Aylesbury on the night of the robbery.

Then aged 28, he was woken by a call at 5am letting him know there had been a burglary near Cheddington.

I said 'what's gone?' and they said 'a train'. An early call generally meant a long day and this was no exception. In those days we got dressed - suit, collar and tie - and off we went.

– Keith Milner, former Thames Valley Police officer

John Woolley (left) and Keith Milner Credit: Steve Parsons/PA Wire

After first collecting evidence on the railtrack, Mr Milner spent nine months attached to the investigation as the officer in charge of exhibits.

He was instrumental during the subsequent court case and worked shoulder to shoulder with Scotland Yard legends such as Leonard "Nipper" Read, later responsible for bringing down the East End gangland empire ruled by the Kray twins.

Twelve of the robbers were jailed for a total of more than 300 years but more than one broke out of prison, including notorious criminal Ronnie Biggs.

The Bridego Bridge near Ledburn in Buckinghamshire which was used in the Great Train Robbery Credit: Steve Parsons/PA Wire

Reynolds returned in 1968, five years after the crime, and was captured in Torquay and jailed for 25 years. He died aged 81 in February.

Last month Biggs insisted he was proud to have been part of the gang.

The famous fugitive, who will celebrate his 84th birthday today, escaped from prison in 1965 and spent 36 years on the run before finally being arrested and jailed in 2001.

John Woolley was a 25-year-old Pc who had been on the job for four years when he discovered Leatherslade Farm, the abandoned hideout the men had used after committing their crime.

Now 75, he explained how he was sent to the property to investigate "suspicious comings and goings" after police received a tip off. Among items officers found at the scene was a Monopoly set which the robbers had used to kill time, playing with real #5 notes taken from their loot.

The original board game was on display today at the commendation ceremony after it was discovered by TV's Antiques Roadshow.

I just happened to be at that place at that time. What I did any of my colleagues could and would have done and perhaps done better. Biggs is perhaps one of the robbers who got some enjoyment, some satisfaction, out of his share of the loot. He did, for a while, live the high life in Brazil, no doubt about that. But he was finally arrested, he is now a very sick man and I'm surprised that he is making all these comments after we have been told time and time again that he is hardly able to speak. Good luck to him, but he is a sick man.

– John Woolley, former Thames Valley Police PC

Coaches of the train involved in the 2.5 million mail robbery Credit: PA Wire

Mr Woolley also said he had been saddened to learn of Reynolds' death and recalled how the criminal mastermind had even sent him a Christmas card one year.

A new book has been published to mark the 50th anniversary, The Great Train Robbery - 50th Anniversary - 1963-2103, said to explain first-hand the complete story of the robbery.

Both Biggs and Reynolds contributed to the book, which has been written by Reynolds' son Nick, along with Biggs' autobiographer Chris Pickard.

Reynolds and Mr Pickard said the book was aimed at "setting the record straight", and putting right any inaccuracies in a tale that has become folklore.

Ms Thornton said: "The coverage in the newspapers and the discussion is always about the offenders in this notorious crime. I wanted to balance that by thanking the police officers and police staff who played a very important role in making sure that those men were brought to justice 50 years ago."